The so-called artificial marbles prepared by blending a resin such as an acrylic resin or an unsaturated polyester resin with an inorganic filler such as aluminum hydroxide or magnesium hydroxide has not only aesthetic properties similar to those of a natural stone but also conveniences such as lightweight and a good workability, and for these reasons, the artificial marbles have rapidly been spread mainly as interior materials, particularly sanitary materials.
In these artificial marbles, an inorganic hydrate which can also function as a flame retardant is blended in a high ratio, and therefore they are recognized to be a flame-retardant material under the Building Standards Act in Japan. However, the artificial marbles cannot be used in places where the employment of an incombustible material or a semi-incombustible material is required.
For the purpose of solving this technical problem, there have been proposed an attempt at making the artificial marbles incombustible by combining aluminum hydroxide with a ground natural stone or another inorganic filler to blend the inorganic component in a high ratio and to relatively decrease a resin content (Japanese Patent Publication No. 30290/1977). Furthermore, there have been proposed a combination of aluminum hydroxide and .alpha.-cristobalite for the purpose of improving a balance between transparency and whiteness of a molded article (Japanese Patent Application Laid-open No. 226543/1985), a combination of aluminum hydroxide and fine silica particles (thermally decomposed silica) for the purpose of preventing the sedimentation of inorganic materials (Japanese Patent Application Laid-open No. 285854/1991), and a combination of a methacrylic resin, aluminum hydroxide and silica (quartz) for the purpose of improving workability and hot water resistance (Japanese Patent Application Laid-open No. 245661/1985).
In any of these prior arts, however, as for the other organic filler which is combined with the inorganic hydrate, its particle diameter has a micrometer order, or even if the particle diameter of its primary particles has a nanometer order, the inorganic filler has been used in a high cohesion state. In consequence, it has been impossible to simultaneously impart the high flame retardancy and the excellent aesthetic properties to the artificial marbles. In addition, if a large amount of the inorganic component is blended at the time of manufacture, the viscosity of the mixture excessively increases. Accordingly, it is practically difficult to blend the inorganic component in a high ratio.
Therefore, in the conventional techniques, it is difficult to impart the high flame retardancy to the artificial marbles, while the excellent aesthetic properties of the artificial marbles are maintained.